Current technologies used in blood banking are extraordinarily labor intensive, prone to human error, and an order of magnitude more expensive per test that those in other clinical laboratories. Coupled with a growing shortage of skilled medical technologists, dwindling supplies of human plasma-derived phenotyping reagents, and an inherent difficulty in fully automating agglutination-based methodologies, the ability to perform rapid and accurate pre-transfusing testing in a cost-effective manner has become a significant challenge. The long-term objective is to use a set of novel molecular technologies to develop a new class of renewable, inexpensive, high-quality blood bank testing reagents that will function in a rapid, high-throughput, automatable assay system. At the core of the proposed technology are red blood cell antigen-specific monoclonal antibodies displayed on the surface of bacteriophage particles. The investigators propose to exploit the naturally-occurring presence of unique DNA sequences within the particles to develop an assay system in which the phenotype of a cell is determined by assaying the genotype of the detecting reagent. Such a strategy will offer extraordinary sensitivity and specificity, will require minute amounts of testing materials and reagents, will be easily adapted to automation, and will be amenable to multiplexing strategies offering the possibility of simultaneous antigen profiling of a red cell sample in a single reaction vessel.